Patients with sufficiently impaired kidney function are required to undergo dialysis to remove toxins from their blood. In general, dialysis involves the removal of toxins from body fluids by diffusing the toxins across a permeable membrane into a toxin-free dialysis solution. In the case of hemodialysis, blood is removed from a patient's body and purified of toxins externally in a dialysis machine. After removal of the toxins, the purified blood is returned to the patient.
Patients receiving hemodialysis typically utilize 75 to 150 liters of prepared dialysis solution three times a week. The largest ingredient in these solutions is water. Reducing water in the dialysis solutions thus reduces the amount of solution which needs to be stored or transported.
Dialysis solutions are currently prepared from separate concentrated solutions. For example, one concentrate, Preparation A, includes a mixture of varied salts, sugars and acids dissolved in water. Another concentrate, Preparation B, is made of sodium bicarbonate dissolved in water. The constituents must be kept separate until soon before hemodialysis because of the tendency for insoluble precipitates to form in the combined solution. As one example, sodium bicarbonate in the presence of various calcium salts, in dry or liquid form, will precipitate calcium carbonate. Typically, these two concentrates are shipped and stored separately in 200 liter drums. When it comes time for administering the hemodialysis to a patient, the concentrates are mixed together in a ratio of 4 liters of Preparation A to 6 liters of Preparation B, along with 110 liters of diluent water. The employment of concentrates speeds and simplifies mixing on site, e.g., in a hospital, relative to time-consuming and complicated dissolution conventionally performed by the concentrate providers.
On the other hand, even in concentrated solutions, the Preparations A and B are themselves bulky and difficult to transport. Moreover, bicarbonate solutions such as Preparation B have a tendency to form carbon dioxide and alter the pH of their solution over extended periods of time, even if not mixed with other reagents. Another logistical problem with preparing dialysis solutions is the need to keep the solutions sterile and endotoxin free.
Various attempts have been made to minimize the logistics required to prepare dialysis solutions. Complete systems have been developed for separating incompatible reagents, water pumping and recirculation systems, pH and conductivity monitors, and water heating components (U.S. Pat. Nos. 5,511,875 & 5,344,231, 4,784,495). In these systems, dissolution is controlled by recirculation of diluent through separate containers of dry powders or acids to form concentrates, which are in turn mixed mechanically to achieve the appropriate concentration. Elaborate mechanisms are used for routing fluids, measuring concentrations and heating prepared solutions.
Other means of preparing dialysate solutions have included systems for mechanically crushing reagents to fine powders and then vaporizing water in the presence of the finely divided, recycled particles (U.S. Pat. No. 4,756,838).
Dialysate solution preparation systems have also packaged together sterile water and powder reagents, separated by a frangible barrier between the compartments. In order to use the solution, the barrier is broken so that the reagents and water can mix together (U.S. Pat. Nos. 4,467,588 and 4,548,606).
Others have also attempted to enhance dissolution of dry reagent formulations by modifying the formulation of the dialysis solution in an attempt to minimize the formation of insoluble precipitates (U.S. Pat. No. 5,122,516).
Significant logistical problems are associated with prior art methods and devices for providing hemodialysis solutions. In addition to reactivity among the constituents of the solutions, transportation of liquid hemodialysis solutions is costly and awkward.
The invention disclosed herein solves these problems and provides tremendous advantages over prior systems.